ITV has threatened to sue Channel 4's Dispatches if it airs an undercover sting purporting to show Coronation Street actors promoting bogus products on Twitter in breach of marketing rules.

The broadcasters squared up on Wednesday following reports that a number of on-screen stars publicised beauty products from a fictitious cosmetics firm set up by the Channel 4 current affairs show.

ITV bosses denied allegations that some Coronation Street actors had received free gifts or engaged in any "unlawful marketing promotion".

The broadcaster has written to Dispatches threatening legal action over the undercover film. An ITV spokeswoman said on Wednesday: "Cast members responded to tweets sent directly to them by some brands to say thank you.

"Contrary to the allegations which have been made, they didn't receive free gifts in return for tweeting or indulge in any kind of unlawful marketing promotion."

It is understood that no date has been set for the transmission of the undercover Dispatches, extracts of which were leaked to the Sun and the Daily Mirror.

The current affairs programme is understood to have sent out a number of "right to reply" letters to individuals featured in its proposed film, but has not briefed the media about their content.

The documentary appears to have been investigating how social media is used to promote products by celebrities. The Advertising Standards Authority states that individuals endorsing products on Twitter should make it clear using symbols "#spons" or "#ad".

According to the Sun and Daily Mirror, programme-makers covertly filmed Coronation Street stars at an event called "Celebrity Retreat" at Manchester's Great John Street hotel. They called their hoax cosmetics firm "Puttana Aziendale," which translates roughly from Italian as "corporate whore", and offered free giveaways to actors.

Some of the supposed luxury cosmetics were bogus, including fake "mistique spray" and a bottle of toner that contained nothing but tap water.

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